Liquid crystal display device and method of manufacturing the same

ABSTRACT

In a method of forming a liquid crystal display device, a black matrix is disposed on a substrate including a switching element formed thereon, a color filter is disposed on the switching element, a pixel electrode is electrically connected to the switching element, and a first alignment layer is disposed on the pixel electrode, to form a first substrate. A second substrate including a second alignment layer is formed. At least one of the first alignment layer and the second alignment layer includes a reactive mesogen. A liquid crystal layer is interposed between the first substrate and the second substrate. A light is irradiated onto the second substrate to provide pretilt angles of liquid crystal molecules of the liquid crystal layer.

This application claims priority to Korean Patent Application No.2009-69001, filed on Jul. 28, 2009, and all the benefits accruingtherefrom under 35 U.S.C. §119, the contents of which are hereinincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the invention relate to a liquid crystaldisplay (“LCD”) device, and a method of manufacturing the LCD device.More particularly, exemplary embodiments of the invention relate to aliquid crystal display (“LCD”) device capable of enhancing afterimagesand reliability, and a method of manufacturing the LCD device.

2. Description of the Related Art

Generally, in a liquid crystal display (“LCD”) device, a voltage isapplied to an electric field generating electrode to provide the liquidcrystal layer with an electric field, and arrangement of liquid crystalmolecules of a liquid crystal layer is controlled in response to theelectric field, thereby displaying images.

The LCD device may be operated with a super vertical alignment (“S-VA”)mode. According to the S-VA technology, liquid crystal molecules andultraviolet (“UV”)-curable particles are injected between first andsecond substrates, and the UV-curable particles are cured to pretilt theliquid crystal molecules under conditions in which a data voltage of awhite gray scale is applied between the first and second substrates.

Polarized ultraviolet light is irradiated to photocrosslinkablecopolymer including a mesogenic group having liquid crystal properties,the mesogenic group being referred as a reactive mesogen (“RM”), toinduce anisotropy to the photocrosslinkable copolymer, and heat isapplied to the photocrosslinkable copolymer to enhance the anisotropy ofan alignment layer, to thereby align liquid crystal molecules.

However, the RM injected between first and second substrates may not beeasily cured at a surface of the alignment layer, and the RM may remainin the liquid crystal layer. The RM remaining in the liquid crystallayer may be cured by light from a backlight of the LCD device, andcured amounts of the RM differ depending on location. Thus, pretiltangles of liquid crystal molecules may not be uniform. As a result,afterimages may appear on a display screen.

BRIEF SUMMARY OF THE INVENTION

Exemplary embodiments of the invention provide a liquid crystal display(“LCD”) device having improved afterimages and reliability.

Exemplary embodiments of the invention also provide a method ofmanufacturing the LCD device.

According to an exemplary embodiment of the invention, there is provideda method of manufacturing an LCD device. In the method, a black matrixis disposed on a substrate including a switching element disposedthereon, a color filter is disposed on the switching element, a pixelelectrode is electrically connected to the switching element, and afirst alignment layer is disposed on the pixel electrode, to form afirst substrate. A second substrate including a second alignment layeris formed. The second substrate faces the first substrate. At least oneof the first alignment layer and the second alignment layer includes areactive mesogen (“RM”). A liquid crystal layer is interposed betweenthe first substrate and the second substrate. A light is irradiated ontothe second substrate to provide pretilt angles of liquid crystalmolecules of the liquid crystal layer.

In an exemplary embodiment of the invention, the reactive mesogen (“RM”)may be cured by irradiating the light.

In an exemplary embodiment of the invention, at least one of the firstalignment layer and the second alignment layer may include at least oneselected from the group consisting of polyamic acid, polyimide, andpolysiloxane.

In an exemplary embodiment of the invention, at least one of the firstalignment layer and the second alignment layer may include an initiatorto promote a curing reaction of the reactive mesogen.

In an exemplary embodiment of the invention, the reactive mesogen (“RM”)may include a compound represented by the following Chemical Formula 1:

Y₁-A₁-Y₂  <Chemical Formula 1>

where each of Y₁ and Y₂ represents an acrylate group or a methacrylategroup, A₁ represents a biphenyl group, a terphenyl group, or anaphthalene group, and each hydrogen atom of A₁ is replaceable with F,Cl, CH₃, or OCH₃.

In an exemplary embodiment of the invention, at least one of the firstalignment layer and the second alignment layer may include about 0.1percent by weight to about 20 percent by weight of the reactive mesogen(“RM”) based on a total weight of the first alignment layer or thesecond alignment layer.

In an exemplary embodiment of the invention, the initiator may includeat least one selected from the group consisting of benzyl dimethylketal, α-amino acetophenone, and 1-hydroxy cyclohexyl phenyl keton.

In an exemplary embodiment of the invention, at least one of the firstalignment layer and the second alignment layer may include about 0.01percent by weight to about 1 percent by weight of the initiator based ona total weight of the reactive mesogen (“RM”).

In an exemplary embodiment of the invention, in irradiating the lightonto the second substrate, about 0.01 joule (J) to about 10 J of anunpolarized UV light may be irradiated at a condition in which anelectric field is applied to the liquid crystal layer.

In an exemplary embodiment of the invention, about 15 J to about 100 Jof an unpolarized UV light may be further irradiated at a condition inwhich an electric field is not applied to the liquid crystal layer,after irradiating the unpolarized UV light at a condition in which anelectric field is applied to the liquid crystal layer.

In an exemplary embodiment of the invention, about 0.1 J to about 1 J ofan unpolarized UV light may be further irradiated at a condition inwhich an electric filed is not applied to the liquid crystal layer,before irradiating the unpolarized UV light at a condition in which anelectric field is applied to the liquid crystal layer.

According to another exemplary embodiment of the invention, an LCDdevice includes a first substrate including a black matrix disposed on asubstrate including a switching element disposed thereon, a color filterdisposed on the switching element, a pixel electrode electricallyconnected to the switching element and a first alignment layer disposedon the pixel electrode, a second substrate including a common electrodefacing the pixel electrode, and a second alignment layer disposed on thecommon electrode, the second substrate facing the first substrate, atleast one of the first alignment layer and the second alignment layerincluding a reactive mesogen (“RM”), and a liquid crystal layerinterposed between the first substrate and the second substrate andincluding liquid crystal molecules at pretilt angles.

In an exemplary embodiment of the invention, the reactive mesogen (“RM”)may be cured by irradiating a light onto the second substrate.

In an exemplary embodiment of the invention, the pixel electrode mayinclude a first pixel electrode and a second pixel electrode to receivedifferent pixel voltages respectively.

In an exemplary embodiment of the invention, the first alignment layerand the second alignment layer including the cured mesogen may beconfigured to arrange a long axis of liquid crystal molecules of theliquid crystal layer in a perpendicular direction with respect to thesubstrate when an electric field is not applied to the liquid crystallayer.

In an exemplary embodiment of the invention, the liquid crystalmolecules may be tiled by the first alignment layer and the secondalignment layer when an electric field is applied to the liquid crystallayer.

According to the invention, a reactive mesogen (“RM”) and an initiatorare mixed with an alignment layer, not a liquid crystal. Thus,reliability deterioration by elution of remaining RM may be decreased,so that display quality may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the invention will becomemore apparent by describing in detailed exemplary embodiments thereofwith reference to the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating an exemplary embodiment of a methodof manufacturing a liquid crystal display (“LCD”) device, according tothe invention;

FIG. 2 is a plan view illustrating an exemplary embodiment of a firstsubstrate of the LCD device, according to the invention;

FIG. 3 is a cross-sectional view taken along line I-I′ of the firstsubstrate of FIG. 2;

FIG. 4 is a cross-sectional view illustrating an exemplary embodiment ofa process for forming a first alignment layer on the first substrate ofFIG. 3;

FIG. 5 is a cross-sectional view illustrating an exemplary embodiment ofa process for forming a liquid crystal layer on the first alignmentlayer;

FIG. 6 is a cross-sectional view illustrating an exemplary embodiment ofa process for combining the first substrate including the liquid crystallayer disposed thereon, and a second substrate; and

FIGS. 7 and 8 are cross-sectional views illustrating an exemplaryembodiment of a process for providing pretilt angles of liquid crystalmolecules.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. The invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Inthe drawings, the sizes and relative sizes of layers and regions may beexaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or connected to the other element or layer or interveningelements or layers may be present. In contrast, when an element isreferred to as being “directly on” or “directly connected to” anotherelement or layer, there are no intervening elements or layers present.Like numerals refer to like elements throughout. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the invention.

Spatially relative terms, such as “lower,” “upper” and the like, may beused herein for ease of description to describe one element or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. It will be understood that the spatially relative terms areintended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Forexample, if the device in the figures is turned over, elements describedas “lower” relative to other elements or features would then be oriented“upper” relative to the other elements or features. Thus, the exemplaryterm “lower” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used hereininterpreted accordingly.

The terminology used herein is for the purpose of describing particularexemplary embodiments only and is not intended to be limiting of theinvention. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Exemplary embodiments of the invention are described herein withreference to cross-sectional illustrations that are schematicillustrations of idealized exemplary embodiments (and intermediatestructures) of the invention. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, exemplary embodiments ofthe invention should not be construed as limited to the particularshapes of regions illustrated herein but are to include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle will, typically, haverounded or curved features and/or a gradient of implant concentration atits edges rather than a binary change from implanted to non-implantedregion. Likewise, a buried region formed by implantation may result insome implantation in the region between the buried region and thesurface through which the implantation takes place. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the actual shape of a region of a device andare not intended to limit the scope of the invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

All methods described herein can be performed in a suitable order unlessotherwise indicated herein or otherwise clearly contradicted by context.The use of any and all examples, or exemplary language (e.g., “suchas”), is intended merely to better illustrate the invention and does notpose a limitation on the scope of the invention unless otherwiseclaimed. No language in the specification should be construed asindicating any non-claimed element as essential to the practice of theinvention as used herein.

Hereinafter, the invention will be explained in detail with reference tothe accompanying drawings.

FIG. 1 is a flowchart illustrating an exemplary embodiment of a methodof manufacturing a liquid crystal display (“LCD”) device according tothe invention.

Referring to FIG. 1, an alignment layer including a reactive mesogen(“RM”) and an initiator, is formed on a first substrate including apixel electrode including a microslit portion which determines analignment direction of liquid crystal (step S10). A liquid crystal layeris interposed between the first substrate and a second substrate (stepS20). The first substrate is combined with the second substrate so thatthe first and second substrates face each other (step S30). A light isirradiated to the liquid crystal layer to cure the RM of the alignmentlayer, so as to provide a pretilt angle to the liquid crystal (stepS40).

FIG. 2 is a plan view illustrating an exemplary embodiment of a firstsubstrate of the LCD device according to the invention. FIG. 3 is across-sectional view taken along line I-I′ of the first substrate ofFIG. 2.

Referring to FIGS. 2 and 3, an LCD device according to the inventionincludes a first substrate 101, a second substrate (not shown) facingthe first substrate 101, and a liquid crystal layer (not shown)interposed between the first substrate 101 and the second substrate. Aplurality of pixel electrodes 162 and 164 is disposed on a unit pixelarea PA01 of the LCD device, and the pixel electrodes 162 and 164receive pixel voltages that are different from each other.

The pixel electrodes 162 and 164 include a plurality of a microslitportion 161 and 165, respectively, in order to enhance a viewing angleby varying alignment directions of liquid crystal molecules. Analignment layer including a RM and an initiator is disposed on the pixelelectrodes 162 and 164 and/or a common electrode of the secondsubstrate, in order to enhance the response time of liquid crystal,where the liquid crystal is aligned to have a pretilt angle throughultraviolet (“UV”) light curing of the RM of the alignment layer.

The pixel electrodes 162 and 164 are disposed on the unit pixel areaPA01. One of the pixel electrodes 162 and 164, to which a high pixelvoltage is applied, may be denoted as a main pixel electrode, and theother of the pixel electrodes, to which a low pixel voltage is applied,may be denoted as a sub-pixel electrode. In the illustrated embodiment,the main pixel electrode corresponds to a first pixel electrode 162, andthe sub-pixel electrode corresponds to a second pixel electrode 164.

The first and second pixel electrodes 162 and 164 are electricallyconnected to a same gate line GL1, and are electrically connected todifferent data lines DL1 and DL2, respectively. Thus, a pixel of the LCDdevice is driven by one gate line and two data lines (“1G2D”) method.

In the illustrated embodiment, a switching part includes a firstswitching element 122 and a second switching element 124. The firstswitching element 122 electrically connects the first pixel electrode162 to the gate line GL1 and a first data line DL1. The second switchingelement 124 electrically connects the second pixel electrode 164 to thegate line GL1 and a second data line DL2.

Pixel voltages having different levels may be applied to the first andsecond pixel electrodes 162 and 164, respectively. In one exemplaryembodiment, a first pixel voltage applied to the first pixel electrode162 is higher than a second pixel voltage applied to the second pixelelectrode 164. Alternatively, a first pixel voltage applied to the firstpixel electrode 162 may be lower than a second pixel voltage applied tothe second pixel electrode 164. When levels of the first and secondpixel voltages are appropriately adjusted, an image viewed from a sideof a display screen of the LCD device, may have, display characteristicsclose to an image viewed from the front of the display screen of the LCDdevice. Moreover, a display quality may be substantially uniformindependently from the viewing angle, so that the side visibility of theLCD device may be enhanced.

The first substrate 101 includes the gate lines GL1 and GL2, the datalines DL1 and DL2, a plurality storage lines (not shown), the first andsecond switching elements 122 and 124, a black matrix 150, a colorfilter 160, the first and second pixel electrodes 162 and 164, and thefirst alignment layer (not shown).

The first substrate according to the invention has a black matrix onarray (“BOA”) structure including the black matrix and the color filter,which are disposed on an array substrate. The BOA structure may cover(e.g., overlap) an area covered by a metal line or a black matrix wherea RM does not react when an UV light is irradiated to the substrate. Thesecond substrate of the invention includes a transparent commonelectrode so that an entire surface of a substrate may be exposed to anUV light.

In an exemplary embodiment of a method of forming a first substrate andreferring to FIGS. 1 and 2, a gate metal is deposited on a first basesubstrate 110 including, for example, a glass material, and then thedeposited gate metal is etched to form the gate lines GL1 and GL2. Thegate lines GL1 and GL2 are formed on the first base substrate 110longitudinally extended in parallel with a row direction D1. A portionof the gate line GL1 forms a gate electrode 112 having a protrudingshape, where the gate electrode 112 extends from a main portion of thegate line GL1. The gate line GL1 which includes the gate electrode 112,is a unitary indivisible member of the first substrate 101. A gateinsulation layer 121 is formed on the gate lines GL1 and GL2.

In the method of forming the first substrate, a semiconductor layer anda source metal layer are sequentially formed on the gate insulationlayer 121, and are etched to form the data lines DL1 and DL2, a sourceelectrode 141, a channel layer 131, and a drain electrode 143. The datalines DL1 and DL2 are longitudinally extended in a substantially columndirection D2, on the gate insulation layer 121. The source electrode 141is extended from the first data line DL1 adjacent to a crossing area ofthe gate line GL1 and the data line DL1, and the source electrode 141 isoverlapped with a portion of the gate electrode 112. A portion of thedrain electrode 143 adjacent to the source electrode 141 is disposed tooverlap with the gate electrode 112, and a portion of the drainelectrode 143 is extended toward the unit pixel area PA01. The sourceelectrode 141 extends from a main portion of the data line DL1. The dataline DL1 which includes the source electrode 141, is a unitaryindivisible member of the first substrate 101.

The gate lines GL1 and GL2 and the data lines DL1 and DL2 cross witheach other to define a substantially rectangular region, and the firstand second pixel electrodes 162 and 164 are disposed on the rectangularshaped region. In the illustrated embodiment, the rectangular region maybe defined as the unit pixel area PA01. Alternatively, the unit pixelarea PA01 may have various shapes such as a Z-shape.

The gate electrode 112, the gate insulation layer 121, the channel layer131, the source electrode 141, and the drain electrode 143 define thefirst switching element 122 including three terminals. The secondswitching element 124 may include a gate electrode 114, a gateinsulation layer 121, the channel layer 131, a source electrode 142, anda drain electrode 144.

In the method of forming the first substrate, a passivation layer 151covering (e.g., overlapping an entire of) the date line DL1 is formed.

The black matrix 150 is formed on the first base substrate including thegate lines GL1 and GL2, the data lines DL1 and DL2, the first and secondswitching elements 122 and 124 and the passivation layer 151 formedthereon. The black matrix 150 shields a light passing through the firstsubstrate 101 to be applied to the liquid crystal layer.

The color filter 160 is disposed directly on the passivation layer 151.The color filter 160 may include a first color filter, a second colorfilter, and a third color filter. The first, second, and third colorfilters represent different colors, respectively. In one exemplaryembodiment, the first color filter may represent a red color, the secondcolor filter may represent a blue color, and the third color filter mayrepresent a green color.

A contact hole is formed extending completely through the color filter160 and the passivation layer 151, to expose a portion of the drainelectrode 143.

An optically transparent and electrically conductive material layer suchas indium tin oxide (“ITO”), indium zinc oxide (“IZO”), etc., isdeposited on the color filter 160. The optically transparent andelectrically conductive material layer makes contact with the drainelectrode 143 through the contact hole. The optically transparent andelectrically conductive material layer is etched to form the first andsecond pixel electrodes 162 and 164.

In the illustrated embodiment, in order to enhance a viewing angle, aviewing angle enhancing technology may be applied to the first andsecond pixel electrodes 162 and 164. In one exemplary embodiment, atechnology dividing a pixel area into a plurality of domains havingdifferent alignment directions, may be employed in the unit pixel areaPA01.

In one exemplary embodiment, in order to form the domains, the first andsecond pixel electrodes 162 and 164 may respectively include a pluralityof supporting electrodes 163 and 167, and a plurality of microslitportions 161 and 165. Portions of the supporting electrodes 163 and 167may be disposed to be respectively parallel to the row direction D1 andthe column direction D2, such that each of the supporting electrodes 163and 167 has a cross shape. Each of the microslit portions 161 and 165may be respectively extended along a first oblique line direction D3 anda second oblique line direction D4, which are inclined with respect tothe row direction D3 and the column direction D3 by an angle of about 45degrees. Each of the microslit portions 161 and 165 may be formed tohave different extended directions in each of domains. The microslitportions 161 and the supporting electrodes 163 collectively form aunitary indivisible first pixel electrode 162. Similarly, the microslitportions 165 and the supporting electrodes 167 collectively form aunitary indivisible second pixel electrode 164.

FIG. 4 is a cross-sectional view illustrating an exemplary embodiment ofa process for forming a first alignment layer on the first substrate ofFIG. 3.

Referring to FIG. 4, a first alignment layer 171 covering the first andsecond pixel electrodes 162 and 164 is formed. The first alignment layer171 overlaps an entire of the first base substrate 110 and forms anuppermost layer of the first substrate 101. The first alignment layer171 is coated on the first and second pixel electrodes 162 and 164, andthen cured. A material that may be used for the first alignment layer171 may include a polyimide compound, a polyamic acid compound, apolysiloxane compound, a polyvinyl cinnamate compound, a polyacrylatecompound, a polymethacrylate compound and the like. The first alignmentlayer 171 may preferably include a polyimide compound, a polyamic acid,a polysiloxane compound and the like. These aforementioned materials canbe used alone or in a combination thereof.

The first alignment layer 171 may include an RM and an initiator.

A mesogen is defined as a photocrosslinkable copolymer including amesogenic group having liquid crystal properties. The anisotropy of themesogen is induced by irradiating polarized UV light to the mesogen, andthe orientation of the mesogen is enhanced through a heat treatment. Themesogenic group has liquid crystal properties in a specific temperaturerange or in a specific solution. The RM may include a material or acompound, which is capable of inducing a liquid crystal phase reaction,and may have a shape of, for example, a bar, a banana, a board and adisk. In one exemplary embodiment, the RM may include a reactive groupsuch as acrylate, methacrylate, epoxy, oxetane, vinyl-ether, styrene,thiol-ene, etc.

The RM may include a compound represented by the following ChemicalFormula 1.

Y₁-A₁-Y₂  <Chemical Formula 1>

In the above chemical formula, each of Y₁ and Y₂ represents an acrylategroup or a methacrylate group, A₁ represents a biphenyl group, aterphenyl group, or a naphthalene group, and each hydrogen atom of A₁may be replaced with F, Cl, CH₃, or OCH₃.

Examples of a material that may be used for the RM may include compoundsrepresented by the following Chemical Formulas 2 to 8. However, the RMshould not be construed as limited to the examples set forth herein.

The content of the RM may be about 0.1% to about 20% by weight based onthe respective total weight of the first alignment layer, or a secondalignment layer. When the content of the RM is less than about 0.1% byweight, the RM may not function in forming an alignment layer. When thecontent of the RM is greater than about 20% by weight, liquid crystalmolecules having a pretilt angle may be excessively increased.

The initiator is used to promote a curing reaction of the RM. Theinitiator includes a material having a wavelength between about 300nanometers (nm) and about 400 nanometers (nm). The initiator of theinvention absorbs an UV light having a long wavelength range of about365 nm, to be decomposed into a radical so that photopolymeriationreaction is promoted. When an alignment layer includes the initiator,photopolymeriation reaction may be promoted by UV light having a longwavelength range. Thus, an UV light having a short wavelength rangefatal to other organic materials, may not be used to reduce oreffectively prevent damage to the organic materials.

Examples of the initiator may include benzyl dimethyl ketal(Irgacure-651, Ciba, Switzerland), α-amino acetophenone (Irgacure-907,Ciba, Switzerland), 1-hydroxy cyclohexyl phenyl keton (Irgacure-184,Ciba, Switzerland) and the like. These materials can be used alone or ina combination thereof.

The content of the initiator may be about 0.01% by weight to about 1% byweight based on the total weight of the RM. When the content of theinitiator is less than about 0.01% by weight, a reactivity of theinitiator is insignificant. When the content of the initiator is greaterthan about 1% by weight, the initiator functions as impurities to induceafterimages.

According to the invention, the RM and the initiator of the alignmentlayer material are not mixed with the liquid crystal molecules, but arecured by the UV light to form the first alignment layer 171 and thesecond alignment layer (not shown). Thus, reliability deterioration byelution of remaining RM may be decreased.

FIG. 5 is a cross-sectional view illustrating an exemplary embodiment ofa process for forming a liquid crystal layer on the first alignmentlayer 171.

Referring to FIG. 5, a liquid crystal 300 is dropped on the firstalignment layer 171 including the RM and the initiator, to form a liquidcrystal layer 301.

FIG. 6 is a cross-sectional view illustrating an exemplary embodiment ofa process for combining the first substrate 101 including the liquidcrystal layer 301 formed thereon, and a second substrate.

Referring to FIG. 6, the second substrate 201 includes a second basesubstrate 210, a common electrode 220, and a second alignment layer 261.The common electrode 220 may include substantially the same material asthe first and second pixel electrodes 162 and 164. The common electrode220 may be a single continuous layer (e.g., unitary and indivisible) notincluding slit portions.

The second alignment layer 261 is formed on the common electrode 220,and forms a lowermost layer of the second substrate 201. The secondalignment layer 261 may include substantially the same material as thefirst alignment layer 171. The second alignment layer 261 including theRM and the initiator, may be formed by a process identical to a processfor forming the first alignment layer 171.

Before an electric field is applied between the first and second pixelelectrodes 162 and 164, and the common electrode 250, a long axisdirection of liquid crystal 300 (hereinafter referred to as a directorof liquid crystal) may be substantially perpendicular to the firstsubstrate 101 and the second substrate 201.

FIGS. 7 and 8 are cross-sectional views illustrating an exemplaryembodiment of a process for providing pretilt angles of liquid crystalmolecules.

When a respective pixel voltage is applied to the first and second pixelelectrodes 162 and 164, and when a common voltage is applied to thecommon electrode 220, the director of the liquid crystal 300 is tiltedto be parallel to the horizontal direction (e.g., parallel to a plane ofthe first substrate 101 and the second substrate 201). In order to fullytilt the director of the liquid crystal 300 to be parallel, the pixelvoltage and the common voltage may be increased, or may be decreasedgradually.

Referring to FIG. 7, about 0.1 joule (J) to about 10 J of an unpolarizedUV light 7 is irradiated directly onto the second substrate 201 at acondition in which an electric field is applied to the liquid crystallayer 301. The RM of the first and second alignment layers 171 and 261is cured in response to the unpolarized UV light 7, and determines thedirectionality of the liquid crystal 300 directly adjacent to the curedRM.

Referring to FIG. 8, the liquid crystals 300 a and 300 b adjacent to thecured RM 400 of a surface of the first and second alignment layers 171and 261, respectively, may be pre-arranged in the horizontal directionor pre-arranged at an inclined angle with respect to surfaces of thecured RM 400. Thus, when an electric field is not applied to the liquidcrystal layer 301, liquid crystals 300 may be arranged as shown in FIG.8. In exemplary embodiments, liquid crystals 300 a and 300 b are alignedin a horizontal direction or have an inclined angle with respect tosurfaces of the cured RM 400 of the first and second alignment layers171 and 261. The liquid crystal 300 c disposed farther from the cured RM400 is gradually arranged perpendicular with respect to surfaces of thecured RM 400 and planes of the first substrate 101 and the secondsubstrate 201.

In the illustrated embodiments described above, RM is easily cured at asurface of the alignment layer. Additionally, the cured RM is not mixedwith the liquid crystal layer and does not remain in the liquid crystallayer. Thus, pretilt angles of liquid crystal molecules of the liquidcrystal layer may be substantially uniform.

Due to the determined directionality arrangement of the liquid crystal300, the response time of the liquid crystal 300 may be improved.Moreover, arrangement directions of the liquid crystal are various, sothat a viewing angle may be enhanced.

According to another exemplary embodiment, after irradiating about 0.1 Jto about 10 J of an unpolarized UV light 7 on the second substrate 201at a condition in which an electric field is applied to the liquidcrystal layer 301, about 15 J to about 100 J of an unpolarized UV light7 may be irradiated on the second substrate 201 at a condition in whichan electric field is not applied to the liquid crystal layer 301.

Due to further irradiating an unpolarized UV light 7 on the secondsubstrate 201 at a condition in which an electric field is not appliedto the liquid crystal layer 301 after irradiating an unpolarized UVlight at a condition in which an electric field is applied to the liquidcrystal layer, unreacted RM of the uncured first and second alignmentlayers 171 and 261 may be removed, so that the content of remaining RM400 after curing may be reduced to be less than about 3% by weight basedon the respective total weight of the first alignment layer 171, or thesecond alignment layer 261.

According to still another exemplary embodiment, about 0.1 J to about 1J of an unpolarized UV light 7 is irradiated on the second substrate 201at a condition in which an electric field is not applied to the liquidcrystal layer. Then, about 0.1 J to about 10 J of an unpolarized UVlight 7 is irradiated at a condition in which an electric field isapplied to the liquid crystal layer 301, and then, about 15 J to about100 J of an unpolarized UV light 7 may be irradiated on the secondsubstrate 201 at a condition in which an electric field is not appliedto the liquid crystal layer 301.

Due to further irradiating an unpolarized UV light 7 on the secondsubstrate 201 at a condition in which an electric field is not appliedto the liquid crystal layer 301 before irradiating an unpolarized UVlight 7 at a condition in which an electric field is applied to theliquid crystal layer, an RM in the uncured first and second alignmentlayers 171 and 261 having high reactivity is firstly reacted to reduceor effectively prevent afterimages, so that uniformity of a displaydevice may be improved.

The RM of the uncured first and second alignment layers 171 and 261 iscured to determine the directionality of the liquid crystal 300 adjacentto the cured RM 400 by irradiating an unpolarized UV light 7 at acondition in which an electric field is applied to the liquid crystallayer 301. Then, unreacted RM of the uncured first and second alignmentlayers 171 and 261 is removed by irradiating an UV light 7 at acondition in which an electric field is not applied to the liquidcrystal layer 301 so that the content of remaining RM after curing maybe reduced by less than about 3% by weight based on the respective totalweight of the first alignment layer 171, or the second alignment layer261.

According to the illustrated embodiments of an LCD device and a methodof manufacturing the LCD device of the invention, an alignment layerincluding a RM and an initiator may be employed to provide pretiltangles of liquid crystal molecules in a display device having a BOAstructure. Thus, afterimages due to a remaining RM in a display screenmay be prevented or reduced, so that display quality may be improved.

An LCD device structure including the liquid crystal molecules atpretilt angles, may be formed by forming an alignment layer including aRM and an initiator. The liquid crystal molecules at pretilt angles of afinal LCD device is considered a structural characteristic of the finalLCD device. Since the liquid crystal molecules at pretilt angles isimparted by the formed alignment layer having specific materialcharacteristics during a manufacturing process, such manufacturingprocess of forming the alignment layer is considered to impart thedistinct structural characteristic of the liquid crystal molecules atpretilt angles in the final LCD device.

Since the liquid crystal molecules at pretilt angles in the LCD deviceis imparted by forming an alignment layer including the RM and theinitiator, through disposing an alignment layer material includinguncured RM and the initiator on a base substrate, disposing a liquidcrystal layer on the formed alignment layer material, thereby forming anLCD structure including the alignment layer material and the liquidcrystal layer, and curing the alignment layer material of the LCDstructure, such a process is considered as imparting the distinctstructural characteristic of the liquid crystal molecules at pretiltangles in the final LCD device.

Additionally, since the liquid crystal molecules at pretilt angles inthe LCD device is imparted by curing the alignment layer material of theLCD structure to form cured RM not mixed with liquid crystal moleculesof the liquid crystal layer, through irradiating a UV light onto the LCDstructure including the alignment layer material and the liquid crystallayer disposed thereon, where directionality (e.g., pretilt) of theliquid crystal directly adjacent to the cured RM is thereby determined,such a process is also considered as imparting the distinct structuralcharacteristic of the liquid crystal molecules at pretilt angles in thefinal LCD device.

The foregoing is illustrative of the invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthe invention have been described, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the invention. Accordingly, all such modifications areintended to be included within the scope of the invention as defined inthe claims. In the claims, means-plus-function clauses are intended tocover the structures described herein as performing the recited functionand not only structural equivalents but also equivalent structures.Therefore, it is to be understood that the foregoing is illustrative ofthe invention and is not to be construed as limited to the specificexemplary embodiments disclosed, and that modifications to the disclosedexemplary embodiments, as well as other exemplary embodiments, areintended to be included within the scope of the appended claims. Theinvention is defined by the following claims, with equivalents of theclaims to be included therein.

1. A method of manufacturing a liquid crystal display (LCD) device, themethod comprising: forming a first substrate comprising: a black matrixdisposed on a base substrate including a switching element disposedthereon, a color filter disposed on the switching element, a pixelelectrode electrically connected to the switching element, and a firstalignment layer disposed on the pixel electrode; forming a secondsubstrate comprising: a second alignment layer, the second substratefacing the first substrate, wherein at least one of the first alignmentlayer and the second alignment layer comprises a reactive mesogen;forming a liquid crystal layer interposed between the first substrateand the second substrate; and irradiating a light onto the secondsubstrate to provide pretilt angles of liquid crystal molecules of theliquid crystal layer.
 2. The method of claim 1, wherein the reactivemesogen is cured by the irradiating the light.
 3. The method of claim 1,wherein at least one of the first alignment layer and the secondalignment layer comprises at least one selected from the groupconsisting of polyamic acid, polyimide, and polysiloxane.
 4. The methodof claim 1, wherein at least one of the first alignment layer and thesecond alignment layer comprises an initiator to promote a curingreaction of the reactive mesogen.
 5. The method of claim 1, wherein thereactive mesogen comprises a compound represented by the followingChemical Formula 1,Y₁-A₁-Y₂  <Chemical Formula 1> wherein each of Y₁ and Y₂ represents anacrylate group or a methacrylate group, Al represents a biphenyl group,a terphenyl group, or a naphthalene group, and each hydrogen atom of Alis replaceable with F, Cl, CH₃, or OCH₃.
 6. The method of claim 5,wherein at least one of the first alignment layer and the secondalignment layer comprises about 0.1 percent by weight to about 20percent by weight of the reactive mesogen, based on a total weight ofthe first alignment layer or the second alignment layer, respectively.7. The method of claim 4, wherein the initiator comprises at least oneselected from the group consisting of benzyl dimethyl ketal, α-aminoacetophenone, and 1-hydroxy cyclohexyl phenyl keton.
 8. The method ofclaim 7, wherein at least one of the first alignment layer and thesecond alignment layer comprises about 0.01 percent by weight to about 1percent by weight of the initiator, based on a total weight of thereactive mesogen.
 9. The method of claim 1, wherein the irradiating alight onto the second substrate comprises: irradiating about 0.01 jouleto about 10 joules of an unpolarized UV light at a condition in which anelectric field is applied to the liquid crystal layer.
 10. The method ofclaim 9, further comprising: irradiating about 15 joules to about 100joules of the unpolarized UV light at a condition in which an electricfield is not applied to the liquid crystal layer, after irradiating theunpolarized UV light at the condition in which the electric field isapplied to the liquid crystal layer.
 11. The method of claim 10, furthercomprising: irradiating about 0.1 J to about 1 J of the unpolarized UVlight at the condition in which the electric filed is not applied to theliquid crystal layer, before irradiating the unpolarized UV light at thecondition in which the electric field is applied to the liquid crystallayer.
 12. A liquid crystal display device comprising: a first substratecomprising: a black matrix disposed on a base substrate including aswitching element disposed thereon, a color filter disposed on theswitching element, a pixel electrode electrically connected to theswitching element, and a first alignment layer disposed on the pixelelectrode; a second substrate comprising: a common electrode facing thepixel electrode, and a second alignment layer disposed on the commonelectrode, the second substrate opposite to the first substrate, whereinat least one of the first alignment layer and the second alignment layercomprises a reactive mesogen, at least a portion of which is cured; anda liquid crystal layer interposed between the first substrate and thesecond substrate, and including liquid crystal molecules at pretiltangles based on the cured reactive mesogen.
 13. The LCD device of claim12, wherein the reactive mesogen is cured by irradiating a light ontothe second substrate.
 14. The LCD device of claim 12, wherein at leastone of the first alignment layer and the second alignment layercomprises an initiator to promote a curing reaction of the reactivemesogen.
 15. The LCD device of claim 12, wherein the reactive mesogencomprises a compound represented by the following Chemical Formula 1,Y₁-A₁-Y₂  <Chemical Formula 1> wherein each of Y₁ and Y₂ represents anacrylate group or a methacrylate group, Al represents a biphenyl group,a terphenyl group, or a naphthalene group, and each hydrogen atom of Almay be replaced with F, Cl, CH3, or OCH3.
 16. The LCD device of claim14, wherein the initiator comprises at least one selected from the groupconsisting of benzyl dimethyl ketal, α-amino acetophenone, and 1-hydroxycyclohexyl phenyl keton.
 17. The LCD device of claim 12, wherein thepixel electrode comprises a first pixel electrode and a second pixelelectrode which receive different pixel voltages, respectively.
 18. TheLCD device of claim 12, wherein the first alignment layer and the secondalignment layer including the cured reactive mesogen arrange a long axisof the liquid crystal molecules of the liquid crystal layer in adirection substantially perpendicular with respect to the basesubstrate, when an electric field is not applied to the liquid crystallayer.
 19. The LCD device of claim 18, wherein the liquid crystalmolecules are tilted by the first alignment layer and the secondalignment layer including the cured reactive mesogen, when an electricfield is applied to the liquid crystal layer.